Fault Curves and Features of CNC Machine Tools

September 11, 2023

The fault curve can conceptually represent the relationship between the failure rate and time of a CNC machine. Because this curve is shaped like a bathtub, it is often referred to as a "bathtub curve." It divides the life of CNC machine tools into three phases, namely early failure period, accidental failure period and loss failure period.

In the early failure period, the failure rate of the machine tool exhibits a negative exponential curve function change law. At the beginning, the failure rate is very high, but as the operating time increases, the failure rate decreases rapidly and enters a constant failure rate stage. There are many reasons for early failure rate, such as design flaws, errors in manufacturing and installation, and errors in operation and use. After running and checking out the cause of the failure and eliminating it, the failure rate gradually stabilized. This phase is called the trial run or run-in period.

The early failure period not only occurred in the initial period when new machine tools were put into use, but also early failure period when the machine tool parts were repaired or replaced and put into use again.

Incidental failure period is also called effective failure period. At this stage, the failure rate is the lowest and the failure rate is constant. Under normal circumstances, this stage should not be the fault of the owner. It is the best working period of the product. However, due to improper use, operation errors or other unexpected reasons, it can also cause some malfunctions. In addition, if the safety factor of some components is designed to be small, the upper limit of the load may be encountered during use, and it may be damaged due to overload and cause failure. Therefore, in the occasion of accidental failure, special emphasis should be placed on rational use, strengthening maintenance, avoiding operational errors, and extending the useful life of the machine tool as much as possible.

After entering the wear-out failure period, the failure rate caused by the normal wear of the machine parts, chemical corrosion, physical and electrical performance changes, and fatigue of the material caused the rate of failure to rise again. For CNC machine tools, if various diagnostic techniques can be used to understand the wear and tear of parts and components and take appropriate maintenance or replacement measures before components enter their failure period, they can control the occurrence of wear-out failures, thereby prolonging the actual life of the equipment. .

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Author:

Ms. SU LAN RONG

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